Method for switching optical signals

ABSTRACT

The present invention provides an apparatus (74 &amp; 200) for switching an optical signal from an input optical fiber (210) to one of a plurality of output optical fibers (214 &amp; 216). The apparatus (74 &amp; 200) includes a collimator (76) for collimating an input optical signal into a collimated beam (216) at an angle with respect to a reference and a decollimator (78) for focusing the collimated beam to an output optical signal (220). The present invention also includes a reflector (92, 208, 218, &amp; 222) for reflecting the collimated beam. The reflector (92 &amp; 208) has a plurality of positions for changing the angle of the collimated beam (216) with respect to the reference so that the output optical signal (220) is focused on one of the plurality of output optical fibers (214 &amp; 216).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 08/251,837, filed May 27, 1994 and entitled "Apparatus for SwitchingOptical Signals and Method of Operation," now U.S. Pat. No. 5,444,801.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of optical processingsystems, and more particularly to optical switches used in fiber opticnetworks.

BACKGROUND OF THE INVENTION

In fiber optic systems, various methods have been previously developedfor switching optical signals between fiber optic cables. Thesepreviously developed methods can be classified into three categories:electrical, solid-state, and mechanical.

Electrical switches convert an optical signal to an electrical signaland then switch the electrical signal by conventional switchingtechniques. Electrical switches then convert the electrical signal backinto an optical signal. Electrical switching of optical signals isfaster then when using existing mechanical switches, but is alsosignificantly more expensive. Additionally, electrical switching ofoptical signals is bandwidth limited, i.e., a converted electricalsignal cannot "carry" all of the information in an optical signal. Thislimitation prevents electrical switching of optical signals fromutilizing the full optical bandwidth available with fiber optics, andseverely limits the advantages available when using fiber optics.

Solid-state optical signal switches typically use titanium diffusedlithium niobate devices. Solid-state switches have fast switchingspeeds, less than one nanosecond, and the same bandwidth capacity asfiber optics. Solid-state switches, however, cost 30 to 100 times morethan existing mechanical switches and have insertion losses exceeding 20times those for existing mechanical switches.

Previously developed mechanical switches for switching optical signalsare typically lower in cost than electrical or solid-state opticalswitches, provide low insertion loss, and are compatible with thebandwidth of fiber optics. Currently available optical mechanicalswitches, however, are relatively slow, with switching speeds ofapproximately 5 to 50 ms.

The actuators used in some existing mechanical switches result in theirslow switching speed. Previously developed optical mechanical switchestypically move mirrors or prisms or rotate the fiber to change thesignal path for an optical signal. Alternatively, existing mechanicalswitches change a signal's path by moving the input fiber itself toalign with the desired output fiber. Both of these techniques requiremoving large masses (mirrors or prisms) in a minimum time period.Existing optical mechanical switches may use solenoids and motors orpiezo-electric transducers as the actuators.

Recent developments in network systems, such as SONET and asynchronoustransfer mode (ATM) packet switching systems, require optical signalswitching speeds of 10 μs or less. This speed is approximately 1,000times faster than available through previously developed opticalmechanical switches. Therefore, in order to obtain the benefits of fiberoptic networks, more expensive electrical or solid-state switches mustbe used. Additionally, electrical and solid-state fiber optic switchesexperience losses that affect network function.

SUMMARY OF THE INVENTION

Therefore, a need has arisen for a switch for coupling optical signalsbetween fiber optics that eliminates the problems associated withpreviously developed optical switches.

A need has arisen for a low cost, reliable, fast optical mechanicalswitch for coupling optical signals between optical fibers.

An additional need exists for a fiber optic switch having sufficientisolation between channels.

Yet another need exists for a fiber optic switch with a switching speedof approximately 10 μs or less.

In accordance with the present invention, a fiber optic switch isprovided that substantially eliminates or reduces disadvantages andproblems associated with previously developed optical signal switchingdevices and techniques.

One aspect of the present invention provides an apparatus for switchingan optical signal from an input optical fiber to one of a plurality ofoutput optical fibers. The apparatus includes a collimator forcollimating an input optical signal into a collimated beam at an anglewith respect to a reference and a decollimator for focusing thecollimated beam to an output optical signal. The present invention alsoincludes a reflector for reflecting the collimated beam. The reflectorhas a plurality of positions for changing the angle of the collimatedbeam with respect to the reference so that the output optical signal isfocused on one of the plurality of output optical fibers.

Another aspect of the present invention provides an apparatus forswitching a plurality of optical signals from a plurality of inputoptical fibers to a plurality of output optical fibers. The apparatusincludes a collimator for collimating each input optical signal into acollimated beam at an angle with respect to a reference and adecollimator for focusing each collimated beam to an output opticalsignal. The apparatus further includes a reflector for reflecting eachcollimated beam. The reflector has a plurality of positions for changingthe angle of each collimated beam with respect to its reference so thateach output optical signal is focused on one of the plurality of outputoptical fibers.

Yet another aspect of the present invention provides a method forswitching an optical signal from an input optical fiber to one of aplurality of output optical fibers. The method includes collimating theinput optical signal into a collimated beam at an angle with respect toa reference, and then changing the angle of the collimated beam by anamount. The collimated beam is then decollimated and focused after itsangle has been changed to one of the plurality of output optical fibers.Each amount the angle of the beam changes corresponds to switching thecollimated beam to a different output optical fiber.

The present invention provides numerous technical advantages. Atechnical advantage of the present optical switch is its low cost incomparison to existing optical switches.

The present fiber optic switch provides an additional technicaladvantage of a fast switching speed, at approximately 10 μs for oneembodiment of the invention.

The present switch provides a technical advantage of being configurableinto different types of switches, including one fiber to several fibersor several fibers to several other fibers. The present switch can beconfigured as a reversing bypass or cross-bar switch. The present switchmay be also cascaded to provide a large switch array for switchingoptical signals in a network.

The present optical switch is a reflective surface based system havingless components than previously developed optical mechanical switches,and therefore, is less expensive to build.

The present switch may be manufactured using existing materials andtechniques that contribute to its technical advantage of low cost.

Yet another technical advantage of the present switch is its lowinsertion loss, typically less than 1 dB. The isolation provided by thepresent switch eliminates cross-talk in a network employing the presentswitch.

The present switch provides a technical advantage of being suitable withmany applications of fiber optics. It may be integrated into SONET orATM networks to provide low cost switching.

Yet another technical advantage of the present optical switch is that itmay be used as a variable beam splitter, attenuator, or modulator.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention andadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings in which likereference numbers indicate like features and wherein:

FIG. 1 illustrates the collimation of a beam;

FIG. 2 shows the collimation and decollimation of a beam to shift thespatial location of an image;

FIGS. 3A and 3B illustrate the input and output focal planes for thelenses in FIG. 2;

FIG. 4 depicts an embodiment of the present invention;

FIG. 5 illustrates the input focal plane of the optical switch of FIG.4;

FIGS. 6A and 6B illustrate two configurations of the output focal planeof the optical switch of FIG. 4;

FIG. 7 depicts a single lens embodiment of the present invention;

FIGS. 8A and 8B illustrate a configuration for the focal plane of thesingle lens optical switch of FIG. 7;

FIG. 9 depicts an alternate embodiment of a single lens optical switch;

FIGS. 10A-10C illustrate an embodiment of the present inventionconfigured for reversing bypass operation;

FIGS. 11A-11D show an embodiment of the present invention configured forcross-bar switching;

FIG. 12 illustrates an embodiment of the present invention employingfrustrated total internal reflection (FTIR);

FIGS. 13A and 13B show a cascade of two switches of FIG. 12 to provide a1×4 switch;

FIGS. 14A and 14B show an embodiment of a 1×2 fiber optic switch;

FIG. 15 illustrates an embodiment of the present invention employing asingle lens;

FIG. 16 shows an embodiment of the present invention employing twolenses;

FIG. 17 illustrates an alternate embodiment of the present invention fordouble action switching;

FIG. 18 presents a graph of frustrated total internal reflections as afunction of spacing and angle of incidence;

FIGS. 19A-19C illustrate a 4×4 cross-bar switch configuration employingthe present invention; and

FIG. 20 illustrates a switch array employing the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are illustrated in thefigures, like numerals being used to refer to corresponding parts of thevarious drawings.

FIG. 1 illustrates the collimation of a beam with a lens and is helpfulin understanding the theory and operation of the present switch. FIG. 1includes grid 10 having X-axis 12 and Y-axis 14 for reference only.Collimator or lens 16 is positioned along X-axis 12 at a distance 18from Y-axis 14 at the focal length for lens 16. Focal plane 20 for lens16 is nominally shown in FIG. 1 on Y-axis 14. FIG. 1 also includes animage originating at point 22 along focal plane 20 for lens 16. Theimage at point 22 is displaced from X-axis 12 by displacement 24.

The image at point 22 is collimated into parallel beams 26 by lens 16.Parallel beams 26 include center beam 28, top beam 30, and lower beam32, shown for illustrative purposes only. Lens 16 encodes the spatialposition or displacement 24 with reference to X-axis 12 of point 22 infocal plane 20 to angle θ 34. The spatial position of the image at point22 defines angle θ 34 of collimated beams 26. Angle θ 34 may be definedby the relationship: ##EQU1## Therefore, the spatial position of point22 defines the angle θ 34 of beams 26 with respect to optical X-axis 12.

FIG. 2 shows two collimating lenses placed back to back for transferringan input image at point 22 of input 36 to output 38 at point 39. FIG. 2includes lens 16 of FIG. 1 and decollimator or lens 40 also positionedalong X-axis 12. Lens 40 decollimates parallel beams 26 and decodes theangle of the collimated beams back to a displacement when lens 40focuses the beams at point 39 on focal plane 42 associated with lens 40.

Lenses 16 and 40 placed back to back act as a conventional imaging lenswith their magnification equal to the ratio of their focal lengths. Whenthe focal lengths of lenses 16 and 40 are equal, there is nomagnification, rather the image is merely transferred to output 38.Lenses 16 and 40, with equal focal lengths, form an imaging lens whichhas the property of providing an output image at point 39 that isinverted and reversed from the input image at point 22. Output imagepoint 39 is displaced by displacement 48 from X-axis 12 in accordancewith the relationship described in the discussions of Equation 1.Displacement 48 is equal in magnitude to displacement 24. In this way,the input image point 22 is inverted and reversed at output focal plane42 at image point 39. That is, image point 22 on input focal plane 20 isimaged to output focal plane 42 at an equal but opposite displacement 48from the optical center of lenses 16 and 40 represented by X-axis 12 ofFIG. 2. This concept of spatial encoding of a signal's displacement intoan angle during collimation and subsequent decoding of the angle to thedisplacement during decollimation of the beam can be used to route orswitch optical signals to various output optical channels or fibers.

It is noted that while lenses 16 and 40 are both centered along X-axis12 in FIG. 2, that the lenses need not be in alignment to form animaging lens. Tilting either lens 16 or 40 with respect to X-axis 12merely adds to an imaged signal's displacement on the output focalplane. In a like manner, translating either lens 16 or 40 with respectto X-axis 12 merely effects the coupling efficiency.

FIGS. 3A and 3B illustrate a possible configuration for input focalplane 20 and output focal plane 42 in FIG. 2, respectively. Focal plane20 includes six input images, A through F. Input images A through F maybe terminations for optical fibers. The inputs are arrangedsymmetrically about Y-axis 14 and Z-axis 49, which would be out of thepage in FIG. 2. Input A is shown at position 50, Input B at position 52,Input C at position 54, Input D at position 56, Input E at position 58,and Input F at position 60. Shading has been used to differentiate thesignals at each input.

FIG. 3B shows the configuration for output focal plane 42 of FIG. 2. Asdescribed in discussions related to FIG. 2, the images at input focalplane 20 have been inverted about Y-axis 14 and Z-axis 49 at outputfocal plane 42. In this manner, the outputs corresponding to the inputsof FIG. 3A, designated as the prime of the input, are imaged at outputfocal plane 42 at an opposite distance from Z-axis 49. Therefore, outputfocal plane 42 includes Output A' at position 62, Output B' at position64, Output C' at position 66, Output D' at position 68, Output E' atposition 70, and Output F' at position 72. It is noted that the shadingof the inputs in FIG. 3A has been carried over to the outputs of FIG. 3Bso that the corresponding output location for each input is easilyidentified. Therefore, Input A has the same shading as Output A', as dothe other inputs and outputs for FIGS. 3A and 3B. Based on opticalreciprocity, output focal plane 42 could be used as the input with inputfocal plane 20 forming the output.

FIG. 4 illustrates an embodiment of the present inventive opticalswitch. Optical switch 74 includes a collimator or collimating lens 76and a decollimator or decollimating lens 78. Input 84 is located onfocal plane 82 of collimating lens 76. Output 90 is located on focalplane 88 of lens 78. Reflector 92 is positioned between lens 76 and 78.Reflector 92 has first position 94 and second position 96, and may beembodied in a flat mirror. Reflector 92 may be moved between positions92 and 94 by actuator 97. Actuator 97 may comprise a piezo-electricaldevice that receives electrical control signal 99 that causes actuator97 to move reflector 92 between the two positions. Moving reflector 92between positions 94 and 96 changes the positions of outputs 90 betweenposition 98 and 100, respectively. Several possible configurations foractuator 97 are described in U.S. Pat. No. 5,221,987, entitled FTIRModulator, issued to Laughlin, the inventor of the present invention.U.S. Pat. No. 5,221,987 is expressly incorporated by reference.

FIG. 5 shows a possible configuration for input focal plane 82 using theinput references from FIG. 3A. Input focal plane 82 includes Input A atposition 50, Input C at position 54, Input D at position 56, and Input Fat position 60. The inputs of input focal plane 82 are shown centeredalong Y-axis 14 and Z-axis 49 for reference purposes only, it beingunderstood that the inputs need not be centered nor axially aligned.Input B and E are not depicted for simplicity, but could be shown as inFIG. 3A. With reflector 92 in first position 94, the inputs are centeredabout Z-axis 14 as shown in FIG. 5. Moving reflector 92 to position 96changes the centering of the inputs to virtual axis 102.

FIGS. 6A and 6B depict output focal plane 88 from FIG. 4 when reflector92 is in its first and second positions, respectively. The outputreferences from FIG. 3B shall be used in discussing output focal plane88. FIG. 6A shows output focal plane 88 with reflector 92 in firstposition 94 with the outputs focused about Y-axis 14 and Z-axis 49. Aspreviously described in connection with discussions on FIG. 2, inputfocal plane 82 is reimaged to output focal plane 88 by lenses 76 and 78with the inputs inverted and reimaged about Y-axis 14 and Z-axis 49. Inthis way, Input A at position 50 is reimaged at Output A' at position62, Input C is reimaged at Output C' at position 66, Input D is reimagedto Output D' at position 68, and Input F is reimaged to Output F' atposition 72 in output focal plane 88.

Switching reflector 92 to second position 96 has the effect of changingthe virtual center of input focal plane 82 in FIG. 5 to virtualcenterline 102. A shift in the virtual center of input focal plane 82causes a corresponding shift when the input images are reimaged onoutput focal plane 88. With reflector 92 in second position 94, theoutputs at output focal plane 88 are centered about Z-axis 49. Using thereimaging concepts previously described, Input A is reimaged to OutputA' at position 62, Input C is reimaged to Output C' at position 64,Input D is reimaged to Output D' at position 68, and Input F is reimagedto Output F' at position 70. The shading of inputs and outputs provideseasy identification of the routing of the signals from input to output.

Switch 74 uses reflector 92 and the concepts of optical signal spatialencoding and imaging lenses to switch input signals to a number ofoutput signals by virtually shifting the centerlines of lenses 76 and78. The principal that an input image will be reimaged at an output inequal but opposite amounts about the centerline still applies, exceptthat reimaging is done about a new virtual centerline. This allows for ashift in spatial position and also a rearrangement of the order ofoutputs when compared to the inputs. In this way, optical signals atinput optical fibers terminated at input focal plane 84 may be routed tonumerous output optical fibers terminated at output focal plane 88. Itis noted that reflector 92 for switch 74 is shown with two positions forillustrative purposes only. Reflector 92 may have numerous positionseach providing a different virtual axis for the lenses without departingfrom the inventive concepts of the present invention.

FIG. 7 shows an alternate embodiment of the present invention using asingle lens. Switch 106 includes lens 108 that both collimates anddecollimates light beams. Focal plane 112 of lens 108 contains both theinputs and output signals for switch 106. The input signals to switch106 are represented by point 116, and the output signals are representedby point 118, it being understood that the number of input and outputsignals are not limited to the number shown in FIG. 7. Switch 106 alsoincludes reflector 92 having first position 94 and second position 96,actuator 97, and return reflector 114. The input signals represented bypoint 116 from focal plane 112 are collimated by lens 108 intocollimated beams and reflected by reflector 92. The reflected collimatedbeams are directed to and reflected by return reflector 114. Afterreflection by return reflector 114, the collimated beams are againreflected by reflector 92. These signals are then decollimated by lens108 to output signals represented in FIG. 7 as point 118 in focal plane112.

In one embodiment of switch 106, return reflector 114 is at bias angle 8120 with respect to surface 122, that is perpendicular to focal plane112. Bias angle 8 120 can be used to provide a fixed offset for theposition of the input and output signals in focal plane 112. In thisway, the input signals represented by point 116 are spatially displacedin focal plane 112 to provide the output signals represented by point118.

FIGS. 8A and 8B show focal plane 112 of switch 106 with reflector 92 infirst position 94 and second position 96, respectively. FIG. 8A shows apossible configuration for focal plane 112 having multiple input signalsand multiple output signals and with reflector 92 in first position 94.The input signals are represented by Input A, Input B, and Input C,while the outputs are represented by Output A', Output B', and OutputC'. In the example of FIG. 8A with reflector 92 in first position 94,the input and output signals are centered about Y-axis 14 and Z-axis 49.In this way, Input A at position 124 is reimaged to Output A' atposition 126, and Input B at position 128 is reimaged to Output B' atposition 130. In this example, Input C and Output C' are shown inactivefor the first position for reflector 92. (The position of Output C' ifInput C were active is shown in FIG. 8A for reference purposes only.)Like shading on the associated inputs and outputs is provided forclarity.

Continuing the example of FIG. 8A, FIG. 8B shows the results whenreflector 92 is moved to second position 96, causing focal plane 112 toshift to a virtual center about Y-axis 104. In this way, Input A isreimaged to Output A' at position 132, Input B at position 128 isreimaged to B' at position 130, and Input C at position 134 is reimagedto Output C' at position 136. By the process of optical reciprocity, theoutputs of switch 106 can be the inputs and the inputs can be theoutputs.

FIG. 9 illustrates an alternate embodiment for optical switch 106 ofFIG. 7. Switch 138 includes reflector 92 with positions 94 and 96 andeliminates the need for return reflector 114. Input signals from focalplane 112 represented by point 116 are collimated by lens 108. Thecollimated beams are reflected by reflector 92 and decollimated andfocused by lens 108 to output signals represented by point 118 on focalplane 112. By moving reflector 92 between positions 94 and 96 withactuator 97, the virtual center of the inputs at point 116 and theoutputs at point 118 can be modified for switching the inputs to outputsas shown and described in discussions relating to FIGS. 7 and FIGS. 8Aand 8B.

It is noted that while shifts in a signal's path have been discussed inassociation with shifts about a single axis, that these shifts can takeplace about any or multiple axis without departing from the inventiveconcepts of the present invention.

FIGS. 10A-10C show an alternate embodiment of the present switchconfigured to form a reversing bypass switch. FIG. 10A represents thefunction performed by reversing bypass switch 140. In the first positionof switch 140, Input A couples to Output A' and Input B couples toOutput B'. In the second position, Input A couples to Input B and OutputA' couples to Output B'. Using, for example, switch 106 of FIG. 7, orswitch 138 of FIG. 9, reversing bypass switch 140 may be provided usingthe concepts of the present invention.

Switch 106 of FIG. 7 may be configured to form reversing bypass switch140 of FIG. 10A. By replacing lens 108 with an appropriate lens, such asa gradient index (GRIN) lens, allows switch 106 to provide a reversingbypass function.

FIG. 10B shows the focal plane associated with GRIN lens 141 thatreplaces lens 108 of switch 106 to form reversing bypass switch 140. Bycoupling optical fibers for feedback directly to the focal plane of GRINlens 141, as shown in FIG. 10B, reversing bypass may be achieved.Optical fibers 142 may be coupled to lens 141 by an appropriate indexmatching adhesive to minimize energy loss or refraction as an opticalsignal goes from fiber 142 to lens 141. Optical fibers 142 provide InputA at position 144, Input B at position 146, Output A' at position 148,and Output B' at position 150. Return loop 152 provides a return pathbetween positions 154 and 156, and may also be embodied in an opticalfiber.

With reflector 92 of switch 106 of FIG. 7 in first position 94, focalplane 112, as depicted in FIG. 10B, is centered about Y-axis 14 andZ-axis 49. As previously described, Input A at position 144 is imaged toOutput A' at position 148, and Input B at position 146 is imaged tooutput B' at position 150. In this way, Input A is routed to Output A'and Input B is routed to Output B' as shown in FIG. 10A.

FIG. 10C shows the resulting shift in the virtual axis of focal plane112 of lens 141 to Y-axis 104 and Z-axis 49 when reflector 92 of switch106 is moved to second position 96. Input A at position 144 is imaged tothe input of return loop 152 at position 154. Return loop 152 providesInput A to position 156 of return loop 152, that, in turn, is reimagedto Input B at position 146. Output A' at position 148 is reimaged toOutput B' at position 150. In this way, Input A is routed to Input B andOutput A' is routed to Output B' providing the second position ofreversing bypass switch 140 of FIG. 10A.

In a similar manner; switch 138 of FIG. 9 can be modified to providereversing bypass switch 140.

FIGS. 11A through 11D show an embodiment of the present inventionconfigured to form cross-bar switch 158. In its first position, Input Acouples to Output A' and Input B couples to Output B'. In the secondposition of switch 158, Input A couples to Output B' and Input B couplesto Output A'.

Optical switch 74 of FIG. 4 may be configured to form cross-bar switch158. For switch 74, using an appropriate lens such as a GRIN lens forlens 76 and 78 allows switch 74 to provide the cross-bar function. Lens76 may be embodied in GRIN lens 159, and lens 78 may be embodied in GRINlens 160. FIG. 11B shows input focal plane 163 associated with GRIN lens159. Fibers 142 are coupled directly to focal plane 163 of GRIN lens 159as previously described in connection with discussions of FIGS. 10B and10C. Input focal plane 163 includes Input A at position 161, Input B atposition 162, Output A' at position 164, and Output B' at position 166.

FIG. 11C shows the fiber configuration at focal plane 165 of second lensGRIN 160, including first return loop 170 coupling positions 172 and174, second return loop 176 coupling positions 178 and 180, third returnloop 182 coupling positions 184 and 186, and fourth return loop 188coupling position 190 and position 192. The return loops may be embodiedin optical fibers and may be coupled to focal plane 165 associated withlens 160 by an index matching adhesive as previously described.

With reflector 92 in first position 94, the input signals from lens 159are imaged at line 194 in focal plane 165 associated with lens 160. Inthis way, Input A at position 161 is imaged to position 192 on fourthreturn loop 188. Loop 188 provides Input A to position 190 which, inturn, is reimaged to position 164 at Output A'. Input B at position 162is imaged to position 184 on third return loop 182. Loop 182 providesInput B to position 186 which, in turn, is reimaged to position 166 atOutput B'. In this first position, therefore, Input A is coupled toOutput A' and Input B is coupled to Output B'.

Moving reflector 92 to second position 96 causes the input signals fromlens 159 to be imaged at line 196 on focal plane 165 of lens 161. FIG.11D shows focal plane 82 with return lens 160 focused about line 196.Input A at position 161 is imaged to position 180 of second return loop176. Loop 176 provides Input A to position 178 which, in turn, isreimaged to position 166 at Output B'. Input B at position 162 is imagedto position 172 of first return loop 170. Loop 170 provides Input B toposition 174 which, in turn, is reimaged to position 164 at Output A'.In this manner, Input A is coupled to Output B' and Input B is coupledto Output A'.

Cross-bar switch 158 may be accomplished by looping return fibers fromfocal plane 165 of lens 160 to focal plane 163 of lens 159. An exampleof a configuration of the present invention utilizing return fiberbetween lenses will be described in discussions related to FIGS. 19-19Cbelow.

The present invention as described in discussions on FIGS. 4-11Daccomplishes switching optical signals between input fibers and outputfibers through shifting one or more virtual axis of the system bychanging the position of a reflector between multiple positions.Shifting the virtual axis of an image can also be accomplished by theconcept of frustrated total internal reflection (FTIR).

When light travels from a denser medium, such as glass, into a lessdense medium, such as air, the angle of the light in the less densemedium is greater than when in the denser medium. Total internalreflection is the phenomenon whereby light traveling at an angle in thedenser medium will be perfectly reflected by the interface between thedenser and less dense medium. This perfect reflection or total internalreflection may be frustrated by bringing a second refractor intoproximal contact with the reflecting surface of the denser medium. Theterm "proximal contact" will be further defined in discussions relatedto FIG. 18. The light traveling in the denser medium will pass throughthe reflecting surface and travel into the second refractor. This is theconcept of frustrated total internal reflection (FTIR).

FTIR is described in U.S. Pat. No. 5,221,987. The present inventionemploying FTIR routes the optical energy from one or more input fibersto a plurality of output fibers. The switch routes the energy byfrustrating the total internal reflection in the switch by a variablebut controlled amount.

FIG. 12 illustrates an embodiment of the present optical switchutilizing FTIR. FTIR optical switch 200 includes collimator 76 anddecollimator 78 that may be lenses. Switch 200 includes refractor 202positioned between lenses 76 and 78. Refractor 202 is a right angleprism in the embodiment of switch 200 of FIG. 12, it being understoodthat other configurations for refractor 202 may be suitable for switch200 without deviating from the inventive concepts of the presentinventions. Switch 200 also includes a second refractor or switchplate204 that is used to frustrate total internal reflection in refractor202. Switch 200 also includes actuator 205 for moving switchplate 204into proximal contact with refractor 202. In one embodiment of switch200, actuator 205 is a piezo-electrical device. Configurations foractuator 205 may be found in U.S. Pat. No. 5,221,987. Input signals areprovided to switch 200 by input fiber 210 located in the focal plane forlens 76, and output signals are provided to output fibers 212 and 214located at the focal plane for lens 78.

In the first position of switch 200, switchplate 204 does not touchrefractor 202. The energy from input fiber 210 is collimated into beam216 by collimating lens 76 and beam 216 is introduced into refractor202. Collimated input beam 216 is reflected at reflecting surface 218 ofrefractor 202 by total internal reflection (TIR) and forms primarycollimated output beam 220. Primary collimated output beam 220 isfocused by decollimating output lens 78 and to first output opticalfiber 212.

To accomplish switching from input optical fiber 210 to second outputoptical fiber 214, switchplate 204 is brought into proximal contact withreflecting surface 218 of refractor 202 by actuator 205. This frustratesthe total internal reflection in refractor 202 resulting in inputcollimated beam 216 being transmitted into switchplate 204. Collimatedbeam 216 is reflected from reflective surface 222 of switchplate 204 bytotal internal reflection as secondary collimated output beam 226. It isnoted that total internal reflection at reflective surface 222 is notalways necessary.

Reflective surface 222 of switchplate 204 is at a bias angle θ 223 toinside surface 224 of switchplate 204. Secondary collimated output beam226 leaves refractor 202 at an angle of two times angle 223 θ to that ofprimary collimated output beam 220. Secondary collimated output beam 226is then reimaged by output lens 78 onto second output optical fiber 214.By this method, an optical signal at input optical fiber 210 can beswitched between output optical fibers 212 and 214 by moving switchplate204 into and out of proximal contact with refractor 202. Whenswitchplate 204 is not in proximal contact with refractor 202, theoptical signal from input optical fiber 210 is imaged to first outputoptical fiber 212. When switchplate 204 is brought into proximal contactwith refractor 202, total internal reflection in refractor 202 isfrustrated, thereby causing the optical signal from input optical fiber210 to be imaged to second output optical fiber 214.

Controlling the spacing between switchplate 204 and refractor 202controls the frustration of the total internal reflection by refractor202. The reflections at reflective surface 218 when frustrated bysurface 224 are developed from field theory and have been well defined.The reflection at reflective surface 218 of refractor 202 of switchplate204 is defined as: ##EQU2## where: The subscripts, s and p, refer towaves polarized perpendicular to and parallel to the plane of incidence,respectively.

φ=the angle from the normal in refractor 202 at reflective surface 218;

n₀ =the index of refraction of refractor 202.

n₁ =the index of refraction for the medium between refractor 202 andswitchplate 204.

n₂ =the index of refraction of switchplate 204.

FIG. 18 illustrates the reflection at reflective surface 218 ofrefractor 204 as a function of the spacing between surface 218 andsurface 224 for several typical angles to be encountered at surface 222and as a function of the spacing between refractor 202 and switchplate204. FIG. 18 demonstrates that the degree of frustration of the totalinternal reflection within refractor 202 is a function of the spacingbetween refractor 202 and switchplate 204. Therefore, by bringingswitchplate 204 into proximal contact with refractor 202 (as defined byEquations (2) through (7) and FIG. 18) controls the portion of thecollimated beam that is reflected by refractor 202 and the portionreflected by switchplate 204.

Alternatively, by varying the spacing between refractor 202 andswitchplate 204, an input optical signal from input optical fiber 210may be variably split between output optical fibers 212 and 214 forminga signal splitter. In a similar manner, switch 200 may be used tovariably attenuate an input signal to either output optical fibers 212and 214.

In the preferred embodiment, lenses 76 and 78 are GRIN lenses. Inputoptical cable 210 may be coupled directly to lens 76 and output opticalcables 210 and 214 may be coupled directly to lens 78 by the techniquespreviously identified when using GRIN lenses.

The operation of switch 200 has been described as having an unswitchedposition with switchplate 204 removed from refractor 202 and a switchedposition when switchplate 204 is brought into proximal contact withrefractor 202. With this configuration, switch 200 does not employ FTIRin reflector 202 when unswitched and does when switched. It is notedthat the operation of switch 200 can be reversed without departing fromthe inventive concepts of the present invention. For example, theunswitched condition for switch 200 can be established to be whenswitchplate 204 is in proximal contact with refractor 202 causing FTIRand the switched condition of switch 200 would be when switchplate 204is removed from refractor 202 and FTIR in refractor 202 does not occur.The choice of switched and unswitched conditions for switch 200 does notaffect its performance.

Additionally, actuator 205 of switch 200 has been thus far described asmoving switchplate 204 into and out of proximal contact with refractor202. Actuator 205 may be embodied in any of the transducers described inU.S. Pat. No. 5,221,987 without departing from the inventive concepts ofthe present invention. Actuator 205 can be used to move switchplate intoand out of proximal contact with refractor 202 depending on theconfiguration of the optical switch. In this way, actuator 205 controlsthe spacing between refractor 202 and switchplate 204.

FIG. 13A shows an alternate embodiment of the present invention usingFTIR to switch a single input optical fiber to multiple output opticalfibers. Switch 228 includes collimating lens 76 and decollimating lens78. The input to switch 228 is provided by input optical fiber 210 andthe output is provided by output optical fibers 212 and 214 shown, andfibers 230 and 232 hidden in the view of FIG. 13A (see FIG. 13B). Switch228 includes refractor 234 in the form of back to back prisms or arhomboid. Refractor 234 has first reflective surface 218 and secondreflective surface 236. Switch 228 has two switchplates, includingswitchplate 204 and switchplate 237, and two actuators, includingactuator 205 and actuator 233.

The operation of switch 228 of FIG. 13A is similar to that described forswitch 200 of FIG. 12. By bringing switchplate 204 into contact withfirst reflective surface 218 of refractor 234, total internal reflectionat first reflective surface 218 within refractor 234 is frustrated, sothat the optical signal traveling in refractor 234 is shifted, aspreviously described in discussions of FIG. 12. In a similar manner,bringing switchplate 237 into contact with second reflective surface 236of refractor 234, frustrates total internal reflection in refractor 234shifting the optical signal traveling at second reflecting surface 236in refractor 234. Once total internal reflection is frustrated at secondreflecting surface 236, the optical signal in refractor 234 will travelthrough inside surface 238 of switchplate 236 to reflective surface 239where the signal is reflected. Switchplate 237 may also have a biasangle (not explicitly shown) similar bias angle θ 223 on switchplate205. The bias angle on switchplate 237 may be in the same plane as biasangle 8 223 on switchplate 205. In the preferred embodiment, however,the bias angle on switchplate 237 is perpendicular to bias angle θ 223,and, therefore, into the page. By this technique, switchplate 204provides two positions for the optical signal traveling in refractor234, and switchplate 237 provides two positions for the optical signaltraveling in refractor 234. This allows an input beam from input opticalfiber 210 to be switched to four output optical fibers. A possibleconfiguration for the four output optical fibers 212, 214, 230, and 232is shown in FIG. 13B.

It is noted that optical switches 200 and 228 shown in FIGS. 12 and 13A,respectively, may be cascaded, and that each cascade provides additionalsignal routing positions. In this way, an optical signal at inputoptical fiber 210 may be switched to any one of numerous output opticalfibers. It is also noted that the number of switches incorporating thepresent invention that may be cascaded is not limited to the embodimentsshown.

FIG. 14A illustrates another embodiment of the present invention. Switch241 of FIG. 14A is similar to switch 106 of FIG. 7 and includesrefractor 202, switchplate 204 and actuator 205 similar to switch 200 ofFIG. 12. Switch 241 also employs collimating and decollimating lens 242.An input optical signal is provided to switch 241 by input optical fiber210, and the output signal is provided to output optical fibers 212 and214. Similar to optical switch 106 of FIG. 7, switch 241 uses returnreflector 114 shown displaced from refractor 202. Return reflector 114may also have bias angle θ 120 with respect to perpendicular surface122. It is noted that return reflector 114 may be embodied in refractor202 without departing from the inventive concepts of the presentinvention.

Input optical fiber 210 provides an image to lens 242, which, in turn,provides collimated input beam 216 to refractor 202. With switchplate208 removed from reflecting surface 218 of refractor 202, collimatedbeam 216 reflects from surface 218 by total internal reflection andtravels to return reflector 114. Bias angle 120 of return reflector 114causes a shift in the return beam (not explicitly shown). The returnbeam is then again reflected by reflecting surface 218 and travels backto lens 242a that decollimates and focuses the return beam to firstoutput optical fiber 212. Lens 242a is shown offset from lens 242 forillustrative purposes only. Lens 242a may be lens 242 that bothcollimates the input image and decollimates the return optical signal.For some applications of the present invention, it may be desirable tohave separate collimating lens 242 and separate decollimating lens 242a.

To switch the output from output optical fiber 212 to output opticalfiber 214, switchplate 204 is brought into contact with reflectingsurface 218 of refractor 202. This frustrates the total reflection inrefractor 202 and causes beam 216 to reflect from reflecting surface 222of switchplate 204. As described in discussions for FIG. 12, this causesa shift in the return beam that is focused by lens 242a to outputoptical fiber 214.

In this way, an input signal may be switched between two or more outputfibers with a single lens. This eliminates the need and expense of asecond lens making switch 241 less expensive.

FIG. 15 shows another embodiment of the present invention configured asa reversing bypass switch. Switch 244 of FIG. 15 is similar to switches200 and 241 of FIGS. 12 and 14A, respectively. Switch 244 includesrefractor 246 in a right angle prism embodiment. Refractor 246 hasreflective surface 248 for providing a return beam. Switch 244 has lens250 which both provides the input signals and receives the outputsignals. Lens 250 may be a GRIN lens having fibers coupled thereto aspreviously described in connection with the discussions on FIGS. 10B and10C. Switch 244 has switchplate 252 which is similar to the previouslyidentified switchplates and an actuator (not explicitly shown) formoving switchplate 252. Reflecting surface 248 of refractor 246 may havea slight bias angle in order to provide a fixed offset in the returnbeam when routing an optical signal between input and output.

In operation of switch 244 of FIG. 15, input signals are collimated bylens 250 and the collimated signals reflect by total internal reflectionat reflective surface 218 to reflective surface 248. A bias onreflective surface 248 will cause a fixed offset in the collimatedsignals that are returned to reflective surface 218 and on back to lens250. Details on the operation of switch 244 will be described inconnection with FIGS. 10B and 10C. When switchplate 252 is not incontact with surface 218 of refractor 246, Input A at position 144 isrouted to Output A' at position 148, and Input B at position 146 isrouted to Output B' at position 150 as depicted in FIG. 10B. Bringingswitchplate 252 into contact with reflecting surface 218 of refractor246 frustrates total internal reflection in refractor 246 causing ashift in the output beam as previously described and depicted in FIG.10C. In this way, Input A at position 144 is imaged to the input ofreturn loop 152 at position 154. Return loop 152 provides the image toposition 156, that, in turn, is reimaged to Input B at position 142.Output A' at position 148 is imaged to Output B' at position 150. Inthis way, Input A is coupled to Input B and Output A' is coupled toOutput B' forming the second position for reversing bypass switch 140.

FIG. 16 depicts another embodiment of the present invention configuredas a cross-bar switch. Switch 254 of FIG. 16 is very similar to switches200 and 241 of FIGS. 12 and 14A, respectively, and provides a cross-barfunction as previously described in connection with discussions of FIGS.11A-11D. Switch 254 includes refractor 246, switchplate 252, an actuator(not explicitly shown), and lenses 256 and 258. Lens 256 of switch 254may be configured similar to lens 82 of FIGS. 11B and 11D, and lens 258may be configured similar to lens 160 of FIG. 11C. Lenses 256 and 258may be embodied in GRIN lenses as previously described.

In operation of switch 254, input optical signals are provided by lens256 to refractor 246. These signals are reflected by reflecting surface218 to lens 258. Lens 258 reflects the signals by employing return loopsas previously described for lens 160. The reflected signals are alsoreflected by reflective surface 218 and back to lens 256. Additionaldetails on the operation of switch 254 of FIG. 16 will be describedusing FIG. 11B-11D. When switchplate 252 is not in contact with surface218 of refractor 246, Input A at position 161 is imaged to position 192of fourth return loop 188. Return loop 188 provides the image toposition 190, which, in turn, is reimaged to Output A' at position 164.Input B at position 162 is imaged to position 184 of third return loop182 that provides this image to position 186. The image at position 186is then reimaged to Output B' at position 166. In this way, Input A iscoupled to Output A' and Input B is coupled to Output B'.

In order to accomplish cross-bar switching, switch-plate 252 may bebrought into contact with surface 218 of refractor 248. This frustratestotal internal reflection in refractor 246 causing a shift in the imageas previously described. Input A at position 161 is then imaged toposition 180 of second return loop 176. Loop 176 provides the image toposition 178, which, in turn, is reimaged to Output B' at position 166.In a similar manner, Input B at position 162 is imaged to position 172of first return loop 170. Loop 170 provides the image to position 174,which, in turn, is reimaged to Output A' at position 164. In thismanner, Input A is coupled to Output B' and Input B is coupled to OutputA' forming the second position of cross-bar switch 158.

FIG. 17 shows another embodiment of the present invention providing amultiposition switch. Switch 260 includes refractor 246 having totalinternal reflecting surfaces 262, 264, and reflective surface 266.Switch 260 also includes switch plates 268 and 270. The input and outputto switch 260 is provided by lens 272 at surface 266 of refractor 246.An input signal provided by lens 272 will be reflected in refractor 246by FTIR surfaces 262, 264, and reflective surface 266. Providing a biasangle (not explicitly shown) on surface 266 will cause a shifting of thesignal as an output at lens 272. Independently moving switchplates 268an 270 into contact with refractor 246 can accomplish switching ofoptical signals provided by lens 272 as previously described forswitches 200, 228, 241, 244, and 254. It should be recognized that thereflective surface 266 can be replaced with an output lens, and thatrefractor 246 may be cascaded to provide compounded switching.

FIG. 20 shows switching system 276 employing switch array 278.Individual switches 280 of array 278 may be embodied in the presentinvention for switching optical signals. To further describe system 278,first stage 282 will be referred to as the input and second stage 284 ofarray 278 will be referred to as the output, it being understood thatsignals may travel in both directions in system 276. Each switch 280 instage 282 includes multiple inputs 286 which may be optical fibers. Eachswitch 280 in stage 282 is coupled to individual switches 280 of secondstage 284 by intermediate couplings 288. Intermediate couplings 288 mayalso be embodied in optical fibers. Each switch 280 of second stage 284provides output optical signals 290, which may also be embodied inoptical fibers. It is noted that the number of input 286, output 290,and intermediate 288 couplings need not be limited to the number shownin FIG. 18.

In operation of system 276, each switch 280 of first stage 282 switchesan input signal to the appropriate intermediate coupling 288. The signalon the intermediate coupling is then switched by one of the individualswitches 280 in second stage 284 to an appropriate output. Each switch280 receives control signal 292 from controller 294. Controller 294 setsthe position of each switch by triggering the actuator in each switch sothat optical signals are routed between inputs and outputs in theappropriate path. Switching system 276 of FIG. 20 shows that the presentinvention can be used to build a multistage switching system forprocessing optical signals.

FIGS. 19A-19C illustrate a 4×4 cross-bar switch that may be implementedusing the concepts of the present invention. In a cross-bar switch, eachof four inputs can be routed to each of four outputs. Switch 300 of FIG.19A-19C can be implemented using any two lens embodiment of the presentinvention previously discussed. Switch 228 of FIG. 13A is one embodimentof the present invention that may be used to implement cross-bar switch300 of FIG. 19A-19C. Switch 300 requires a switch that has two lensesand two switchplates in order to achieve switching four inputs to anyone of four outputs.

FIG. 19B represents a possible configuration for the input focal planeassociated with lens 76 in FIG. 13A. In the preferred embodiment, lens76 is GRIN lens 301 having associated focal plan 302. The inputs atfocal plane 302 are designated as Input A at position 304, Input B atposition 306, Input C at position 308, and Input D at position 310. Eachof these inputs may be provided to focal plane 302 of lens 301 by, forexample, an optical fiber. The optical fiber may be attached to lens 301by an appropriate index matching adhesive as has been previouslydescribed for coupling optical fibers to a GRIN lens.

FIG. 19C represents the configuration for the output focal planeassociated with lens 78 in FIG. 13A. In the preferred embodiment, lens78 is GRIN lens 311 having focal plane 312. Output focal plane 312 oflens 311 includes Output A' at position 314, Output B' at position 316,Output C' at position 318, and Output D' at position 320. Each of theoutput locations on lens 311 has an optical fiber appropriately coupledto it.

FIG. 19A represents the relationships between input focal plane 302 andoutput focal plane 312 for cross-bar switch 300. To achieve thecombinations of the signals in switch 300, return loops a 314, b 316,and c 318 are required. Each of the return loops will route a signalreceived at output focal plane 312 back to input focal plane 302 so thatoperation of cross-bar switch 300 may be achieved.

Returning to FIGS. 19B and 19C, a configuration for the orientation ofthe return loops with the inputs and outputs is shown. On input focalplane 302, return loop a 314 is at position 320, return loop b 316 is atposition 322, and return loop c 318 is at position 324. Thecorresponding configuration for the return loops in output focal plane312 are shown in FIG. 19C. Return loop a 314 is at position 326, returnloop b 316 is at position 328, and return loop c 318 is at position 330.

FIG. 19A also demonstrates how the imaging of signals within cross-barswitch 300 occurs. Vertical axis 332 is provided as a reference betweenthe location of the inputs on input focal plane 302 and the outputs onoutput focal plane 312. Matrix 334 has been superimposed on switch 300to aid in explaining the routing of signals from input focal plane 302to output focal plane 312. Row 336 represents the condition of switch300. As previously noted, switch 300 may be implemented with twoswitchplates. The condition of the switchplates is represented by thepair of numbers in row 336. For example, the condition 0,0 representsswitch 300 with both switchplates open, with open being set arbitrarilywith switchplate in proximal contact with the refractor, it beingunderstood that open could be set for when the switchplate is not inproximal contact with the refractor. Therefore, for example, in column338, the designation 0,0 refers to both switches as open, and in column340, 1,0 refers to the first switchplate closed and the second switchopen. The remaining columns of matrix 334 are self explanatory.

The horizontal lines in matrix 334 illustrate the virtual axis for thesignals for the switch for the four switch positions of row 336. Axis342 is the virtual axis for the switch in 0,0 state, virtual axis 344 isthe virtual axis for the switch in state 1,0, virtual axis 346 is thevirtual axis for the switch in state 0,1, and virtual axis 348 is thevirtual axis for the switch in state 1,1.

The entries within matrix 334 represent the position on output focalplane 312 that the inputs from input focal plane 302 are imaged to. Forexample, for switch state 0,0, Input A at position 304 is aligned withvirtual axis 342 so it is not displaced about virtual axis 342, and isaligned with position 316 on output focal plane 312. Input A, therefore,couples to Output B' at position 316. Input B at position 306 is imagedabout virtual axis 342 to position 314, and, therefore, couples toOutput A'. Input C at position 308 is imaged about virtual axis 342 toposition 326 to return loop a 314. Return loop a 314 provides thissignal back to position 320 of input focal plane 302. Return loop a atposition 320 is imaged about virtual axis 342 to position 318 on outputfocal plane 312 and couples position 320 to Output C'. Therefore, InputC couples to Output D'. The entry "aC" at position 341 in matrix 334indicates that Input C is provided to position 320 by return loop a 314.Input D at position 310 is imaged about virtual axis 342 to position 328at the input of return loop b 316. Return loop b 316 provides the signalback to input focal plane 302 at position 322. Position 322 is thenreimaged about virtual axis 342 to position 318 at Output C' of outputfocal plane 312. Therefore, Input D couples to Output C'. In this way,with switch 300 in state 0,0, each input is coupled to a differentoutput.

Matrix 334 helps understand how the inputs from input focal plane 302are imaged to the outputs on output focal plane 312. In a similarmanner, the other states of switch 300 can be tracked using matrix 334so that each input may be switched to a different output withoutblocking.

Switch 300 of FIG. 19A-19C provides a technical advantage of a cross-barswitch using the present invention. Switch 300 may also be put into anarray of switches to provide, for example, a 16×16 non-blockingcross-bar switching of signals.

It is noted that the present invention may have numerous applications,including, but not limited to: laser Q-switching applications, as alaser safety device, and as an electric chopper wheel. Additionally, thepresent invention may provide switching of RF signals. By using largerscale materials that are transparent to RF signals, advantages of thepresent invention may be achieved for processing RF signals.

The present invention for routing optical signals provides technicaladvantages of low cost and fast switching speeds. The present inventionmay use a common mirror or the concept of frustrated total internalreflection to achieve shifts in a virtual focal plane of an image. Inthis way, an optical signal can be switched, attenuated, modulated orsplit between various outputs.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

What is claimed is:
 1. A method for switching an input optical signal toone of a plurality of output optical locations, the method comprisingthe steps of:collimating the input optical signal into a collimatedbeam; directing the collimated beam to one of the output opticallocations; changing the angle of the collimated beam by a selectedamount in order to direct the beam to a different one of the outputoptical locations; and wherein the changing the angle step furthercomprises changing the angle of the collimated beam by a first amount byreflecting the collimated beam by total internal reflection with a firstrefractor having a reflective surface, changing the angle of thecollimated beam by a second amount by frustrating the total internalreflection of the collimated beam by controlling the spacing between asecond refractor having a reflective surface and the first refractor'sreflective surface, and reflecting the collimated beam with the secondrefractor's reflective surface.
 2. The method of claim 1 furthercomprising the steps of further changing the angle of the collimatedbeam by a third amount by reflecting the collimated beam by totalinternal reflection with a second reflective surface of the firstrefractor.
 3. The method of claim 1 further comprising the steps ofchanging the angle of the collimated beam by a fourth amount byfrustrating the total internal reflection of the collimated beam bycontrolling the spacing between a third refractor having a reflectivesurface and the first refractor's second reflective surface, andreflecting the collimated beam with the third refractor's reflectivesurface.
 4. The method of claim 1 further comprising the step ofchanging the angle of the collimated beam by a third amount byreflecting the collimated beam by total internal reflection with a thirdrefractor having a first reflective surface after reflection of thecollimated beam by one of the first refractor's reflective surface andthe second refractor's reflective surface.
 5. A method for switching aplurality of input optical signals to a plurality of output opticallocations, the method comprising the steps of:collimating each of theinput optical signals into a collimated beam; directing each collimatedbeam to one of the output optical locations; changing the angle of eachcollimated beam by a selected amount in order to direct each beam to adifferent one of the output optical locations; and wherein the changingthe angle step further comprises changing the angle of each collimatedbeam by a first amount by reflecting each collimated beam by totalinternal reflection with a first refractor having a reflective surface,changing the angle of each collimated beam by a second amount byfrustrating the total internal reflection of each collimated beam bycontrolling the spacing between a second refractor having a reflectivesurface and the first refractor's reflective surface, and reflectingeach collimated beam with the second refractor's reflective surface. 6.The method of claim 5 further comprising the steps of further changingthe angle of the collimated beam by a third amount by reflecting thecollimated beam by total internal reflection with a second reflectivesurface of the first refractor.
 7. The method of claim 5 furthercomprising the steps of changing the angle of the collimated beam by afourth amount by frustrating the total internal reflection of thecollimated beam by controlling the spacing between a third refractorhaving a reflective surface and the first refractor's second reflectivesurface, and reflecting the collimated beam with the third refractor'sreflective surface.
 8. The method of claim 5 further comprising the stepof changing the angle of each collimated beam by a third amount byreflecting the collimated beam by total internal reflection with a thirdrefractor having a first reflective surface after reflection of thecollimated beam by one of the first refractor's reflective surface andthe second refractor's reflective surface.
 9. The method of claim 1further comprising the step of decollimating and focusing the collimatedbeam prior to the directing step.
 10. The method of claim 5 furthercomprising the step of decollimating and focusing the collimated beamprior to the directing step.